Space docking systems are utilized to join two or more manned spacecraft together. They are designed to operate in low-Earth-orbit (LEO), in high-Earth-orbit (HEO), on extraterrestrial surfaces, and in deep space locations. Space docking systems and other components of object exposed to space environments include seals in various locations, and these seals are sometimes exposed to the space environment. Some examples include seals at the main interface between two vehicles, at windows, and at fluid and electrical connections. Precious resources necessary for manned and unmanned spaceflight, such as potable water, coolant, and breathable air and refrigerant are retained and confined by seals. Any damage to or other compromising of the seal increases the leak rate and loss of the pressurized fluid or gas.
These seals must withstand multiple uses and hold up against the operational temperate extremes to which they are exposed, and are therefore manufactured from polymers. The polymers are negatively affected by the space environment, including solar radiation in the form of ultraviolet light and reactive elements such as atomic oxygen. The radiation and reactive elements (such as atomic oxygen) to which these seals are exposed compromises the sealing surfaces of the seal in short time spans.
It will be generally appreciated that the intensity of the radiation exposure can change during orbit. For example, FIG. 1A shows a seal 14 in solar inertial orbit about an astronomical object E (such as the planet Earth), the seal 14 having a sealing surface 18 extending or orthogonal to the direction of incoming radiation rays R as for example those coming from a star S (such as the sun). The seal 14 is schematically shown shaped as a trapezoid to show that the nature of solar inertial orbit is easily appreciated. In general, it can be seen that the orientation of the object, here just schematically represented by a seal 14, remains the same relative to a distance object, here represented by the star S, and changes relative to the astronomical body being orbited, here the astronomical body E. Thus, solar inertial orbit, the sealing surface 18 remains orthogonal to the rays R and, thus, unless hidden behind the astronomical object E, the sealing surface 18 receives the full intensity of the rays R.
A local vertical/local horizontal (LVLH) is schematically represented in FIG. 1B and the same numbering and lettering is employed to identify what is schematically represented therein. In LVLH orbit, the seal maintains its orientation relative the astronomical body E being orbited, and, thus, when not hidden behind the astronomical object E, the angle of incidence of the rays R on the sealing surface 18 changes. FIG. 2 shows a small portion of the non-textured sealing surface 18 and a location A thereon exposed to radiation rays during orbit. The relative orientation of point A to the source of solar radiation rays R and other reactive elements changes from point C to D to E. The normalized level of exposure at location A is shown in FIG. 3.
The exposure to radiation rays and to reactive elements in the space environment compromises the sealing surface and the seal in general. These seals tend to be formed of elastomers and the radiation and reactive elements cause the elastomer to become brittle and to erode at the molecular level, shrinking and cracking. Cracked surfaces do not form good seals. This compromises the functioning of the seal. Mission profile and duration is limited by the polymer seal's ability to resist the space environment. Currently, there are no polymer seals that can resist the space environment for greater than 4 days. Therefore, there is a need in the art to improve upon the ability of a seal to resist the detrimental effects of the space environment.